The present invention relates to medical electrodes used for monitoring electrical signals from the skin of a patient and more particularly to disposable electrodes which are prepackaged in a condition ready for use.
Numerous attempts have been made in the prior art to produce a satisfactory disposable medical electrode which would exhibit the electrical characteristics necessary for a low noise signal from the skin of a patient, comfort to the patient during long-term usage, and long shelf life prior to use. In many instances these requirements contradice one another, such that the prior art has achieved success in meeting one requirement only at the expense of another. Thus, for example, long shelf life might be insured by utilizing additional packaging materials. Similarly, the reduction of spurious noise signals, commonly termed motion artifacts, is typically accomplished only at the expense of discomfort to the patient.
As in the case of any disposable item, low cost is an important factor in the design of such electrodes. The prior art electrodes have required the use of multiple packaging techniques in order to insure long shelf life. Thus, the prior art electrode packages typically have included both a protective cover member over the electrolyte and an outer foil container over the entire electrode. This outer foil container has heretofore been necessary for achieving a reasonable shelf life for a pre-gelled electrode. Such packaging necessarily increases the cost of each of the electrodes and, particularly in instances where multiple electrodes are contained in a single foil package, the use of one of the included electrodes subjects the remaining electrodes to evaporation of electrolyte and a resulting requirement that they be used promptly.
The prior art also exhibits the use of barriers to prevent migration or evaporation of electrolyte from the central conductive portion of the electrode to the surrounding area where the electrode is adhesively attached to the patient. These barriers are commonly constructed of rigid material, and are thus subject to being lifted from the skin of the patient when the patient moves, reducing the effectiveness of the moisture barrier, and are uncomfortable to use due to the rigid surface pressed against the patient's skin.
Even in those prior art medical electrodes which sacrifice other characteristics in an effort to provide long shelf life, significant evaporation and migration of electrolyte typically occurs between the cup member used to cover the electrolyte-filled foam member and the carrier sheet to which the cup member has been attached. This migration and evaporation is due primarily to the use of a paper carrier sheet and a simple adhesive attachment to the cup member to this sheet, both of which subject the electrode to electrolyte loss.